The present invention relates to a novel compound having antioxidative power and an antioxidant containing the same compound. More particularly, the present invention relates to a novel compound 7.beta.,11,12-trihydroxy-6,10-(epoxymethano)abieta-8,-11,13-trien-20-one and an antioxidant containing the above comound as well as a method for the preparation of the antioxidant from a natural plant.
It is known that several herbal spices have an effect of preventing oxidation of fats and oils or oleaginous foodstuffs when the spices are blended therewith and a large number of papers have been published reporting the results of the investigations on the antioxidative power of these herbal spices. On the other hand, along with increasing consumption of synthetic antioxidants such as butyl hydroxyanisole (BHA) and dibutyl hydroxytoluene (BHT) as an antioxidative additive in oleaginous foodstuffs, it might be a natural consequence that certain decline was noted once in the investigations on the antioxidative effect of the antioxidants of natural origin such as the herbal spices.
On the contrary, recent social concern and interest in the pharmacy and food industry are directed to the problem of safety of synthetic medicines and food additives and re-evaluation of these synthetic materials in this respect is strongly desired. In accordance with this trend, the effectiveness of natural spices as an antioxidant has come into reconsideration and investigations are now again widely undertaken with activity not only from the standpoint of safety but also as a matter of tastiness when used in foodstuffs.
To give a historical overview on the investigations directed to the detection of the antioxidative ingredients in natural spices, it was the first that the effective ingredient named carnosol extracted from sage, a plant belonging to Salvia carnosa Dougl, as the bitter-tasting component thereof was a phenolic ester compound of a molecular formula C.sub.19 H.sub.26 O.sub.4 containing hydroxyphenanthrene (A. I. White et al., J. Amer. Pharm. Assoc. Sci. Ed., pages 31, 33 and 37, 1942) followed by the report establishing that the above mentioned carnosol is the same compound as picrosalvin which was obtained from sages belonging to the species of Salvia officinalis L. or Salvia triloba L. or rosemary belonging to Rosmarinus officinalis L. as the bitter-tasting component thereof expressed by the following structural formula (C. H. Brieskorn et al., J. Org. Chem., volume 29, page 2293, 1964): ##STR1##
Further, it was determined that rosemary contains a carnosic acid expressed by the following structural formula as reported by Wenkert et al. (E. Wenkert et al., J. Org. Chem., volume 30, page 2931, 1965) as the main terpenic component therein: ##STR2##
Recently, it was suggested that, from the results of the high-speed liquid chromatography into the individual ingredients following washing with water and decolorization, the material extracted from rosemary and sage with a solvent contains certain tasteless and odorless compounds having antioxidative power in addition to the carnosic acid, carnosol and ferruginol known as antioxidants (S. S. Chang et al., J. Food. Sci., volume 42, page 1102, 1977).
Notwithstanding a large number of published reports including the above described ones, the detection and identification of the antioxidative ingredients in herbal spices are only at the very beginning stage of the investigations now on the way and many problems are left unsolved.
Apart from the detection and isolation of the antioxidatively effective ingredients from the herbal spices, it is of course a possible way to use the herbal spice as such as an antioxidant in foodstuffs. This way of using the spices as such is, however, applicable not all of the foods of which strong spicy flavor should be avoided as in the Japanese-style foods since the strong characteristic flavor of the spice usually destroys the taste and flavor of the food per se. Therefore, it is very desirable to extract and concentrate the antioxidative ingredient from the spices and to use the thus concentrated antioxidative ingredient as an antioxidant in foodstuffs. In this connection, there has been proposed in Japanese Patent Publication No. 53-9595 that a spice such as rosemary is directly subjected to the extraction with an alkali solution at a pH of 7 to 10 to give a fraction containing the above mentioned carnosic acid which can be used as an antioxidant. It is noted there that the alkali solution as the extractant should have a pH not exceeding 10 because the material extractable with a strong alkali of a pH higher than 10 has an effect of substantially accelerating oxidation.